使用自定义集合视图布局快速配置动态单元格高度

Question

我有一个自定义集合视图布局，它从下到上为消息传递应用程序加载单元格，但在实现动态单元格高度时遇到问题。我相信我为检索动态单元格高度而连接的协议和委托对每个单元格都有效（我从打印每个 indexPath.item 的高度推断出），除非加载 collectionView 时单元格高度不是他们应该的高度成为。它们都只是一个静态高度（不是 var cellHeight 预设的 80），并且只显示一行文本。

 protocol InvertedStackProtocol: class {
    func collectionView(_ collectionView: UICollectionView, heightForCellAtIndexPath indexPath: IndexPath) -> CGFloat
    }

    class InvertedStackLayout: UICollectionViewLayout, UICollectionViewDelegateFlowLayout {

    var cellHeight: CGFloat = 80

    weak var delegate: InvertedStackProtocol!

    override func prepare() {

        guard let collectionView = self.collectionView else {return}

        for item in 0 ..< collectionView.numberOfItems(inSection: 0) {
            let indexPath = IndexPath(item: item, section: 0)
            let height = delegate.collectionView(collectionView, heightForCellAtIndexPath: indexPath)
            print (height, indexPath.item)
            cellHeight = height
        }

    }

    override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        var layoutAttrs = [UICollectionViewLayoutAttributes]()

        if let collectionView = self.collectionView {
            for section in 0 ..< collectionView.numberOfSections {
                if let numberOfSectionItems = numberOfItemsInSection(section) {
                    for item in 0 ..< numberOfSectionItems {
                        let indexPath = IndexPath(item: item, section: section)
                        let layoutAttr = layoutAttributesForItem(at: indexPath)

                        if let layoutAttr = layoutAttr, layoutAttr.frame.intersects(rect) {
                            layoutAttrs.append(layoutAttr)
                        }
                    }
                }
            }
        }

        return layoutAttrs
    }

    override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
        let layoutAttr = UICollectionViewLayoutAttributes(forCellWith: indexPath)
        let contentSize = self.collectionViewContentSize

        layoutAttr.frame = CGRect(
            x: 0, y: contentSize.height - CGFloat(indexPath.item + 1) * cellHeight,
            width: contentSize.width, height: cellHeight)

        return layoutAttr
    }

    func numberOfItemsInSection(_ section: Int) -> Int? {
        if let collectionView = self.collectionView,
            let numSectionItems = collectionView.dataSource?.collectionView(collectionView, numberOfItemsInSection: section)
        {
            return numSectionItems
        }

        return 0
    }

    override var collectionViewContentSize: CGSize {
        get {
            var height: CGFloat = 0.0
            var bounds = CGRect.zero

            if let collectionView = self.collectionView {
                for section in 0 ..< collectionView.numberOfSections {
                    if let numItems = numberOfItemsInSection(section) {
                        height += CGFloat(numItems) * cellHeight
                    }
                }

                bounds = collectionView.bounds
            }

            return CGSize(width: bounds.width, height: max(height, bounds.height))
            // return CGSize(width: bounds.width, height: height) do this for more exact fit of collection view
        }
    }

    override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
        if let oldBounds = self.collectionView?.bounds,
            oldBounds.width != newBounds.width || oldBounds.height != newBounds.height
        {
            return true
        }

        return false
    }
}

Answer 1

使用此方法更改高度，UICollectionViewCell。

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
    return CGSize(width: 125.0, height: 175.0)
}